1. Field of the Invention
This application is the national phase under 35 U.S.C .sctn.371 of PCT International Application No. PCT/SE99/00081 which has an International filing date of Jan. 20, 1999, which designated the United States of America.
The present invention concerns a rotating filter, said filter including at least two annular filter disks each having a plurality of filter elements and each being carried by a shaft for rotation therewith about an axis perpendicular to a respective central plane of the filter disks, said filter disks being partly submerged in a vessel adapted to contain to a certain level a liquid to be filtered, and said filter further including discharge chute means extending into a space between adjacent filter disks for discharging solids deposited on and removed from facing filtering means of said filter elements.
2. Description of Background Art
WO 94/25140 (U.S. Pat. No. 5,656,162) describes a filter where the filter elements are arranged at a relatively large distance from the shaft and have a relatively small radial extension, thereby giving the filter disks an annular appearance Therefore, a filter of this kind is referred to as a ring filter. In this prior art ring filter, the filtering means of two adjacent filter rings have a common scraper arranged radially outside the filter rings. The tip end of the scraper introduced between the filter rings is axially and radially guided by sliding in a U-shaped guide ring provided between the filter rings and rotating therewith. The scraper also has a substantially U-shaped cross section thereby to serve also as a chute for filter cake removed from the filtering means.
This prior art filter has proved to perform extremely well. However, in certain cases it has been found that, when increasing the radial height of the filter elements, the amount or volume of filter cake material deposited on the filter elements becomes so large that, after its removed from the elements, the material may not be properly discharged by the chute-like scraper running in the rotating, channel-shaped guide ring between two adjacent filter rings. Thus, it may happen that a portion of a filter cake starts to rotate and twist between the scraper and the filtering means (normally a filter cloth) of the filter element and to build up its dimension such that it eventually damages the filter cloth.